The present invention relates to active and semi-active vehicle suspensions and in particular to such suspensions for off-road vehicles.
Vehicle suspensions are characterized in various ways, including the stiffness in roll, single axle articulation, and cross articulation. There are two aspects of a suspension which determine how easily the wheels can move in articulation. One is the damping rate of the dampers, and the other is the spring rate of the springs in the suspension. The term stiffness refers to the spring rate. Therefore the articulation stiffness of the front axle of a vehicle is expressed as a force (expressed as a moment or a linear force) per unit of articulation displacement of the front wheels (expressed as an angular articulation displacement or a linear difference in ride height). The cross articulation stiffness is defined as a force per unit of cross articulation displacement, expressed, for example, as a linear difference in average ride height between two pairs of diagonally opposite wheels.
When a vehicle is travelling over rough terrain it is desirable to allow a high degree of articulation of the wheels, that is vertical movement of the wheels on opposite sides of the vehicle in opposite directions. In particular a high degree of cross articulation is desirable, that is articulation of the front wheels in one direction and articulation of the rear wheels in the opposite direction. This enables the vehicle to maintain traction over highly uneven ground. However this can conflict with the need for firm roll control when the vehicle is travelling at higher speeds on a road, since roll can be considered as articulation of the front and rear axles in the same direction.
This conflict arises, for example, in interconnected fluid suspensions, such as interconnected air suspensions, where the level of interconnection between air strings on opposite sides of the vehicle can be selected to control the level of resistance to articulation.
For example, it is also known from U.S. Pat. No. 5,765,115 to provide an air suspension system in which the air springs of the two rear wheels are interconnected by a pipe, which can be closed and opened by a gate valve, and the air springs of the two front wheels are similarly interconnected. Closing the valves increases roll stiffness of the vehicle, and opening them increases the ease of articulation.
The same conflict arises with the use of anti-roll bars which need to be stiff to provide good roll control on road, but much less stiff to allow sufficient articulation off-road.
This problem has been addressed, for example, by the type of system disclosed in U.S. Pat. No. 4,796,911 which discloses a vehicle with a split anti-roll bar, with a hydraulic de-coupling device between the two halves. A rough road sensor detects when the vehicle is travelling over a rough road and, in response, the two halves of the anti-roll bar are de-coupled from each other so as to increase the ease of articulation. On smooth roads the two halves are coupled together again so as to increase roll stiffness.
A similar conflict arises with dampers which are usually required to provide a relatively high level of damping for on-road use, but a reduced level of damping to increase ease of articulation during off road use. It is well known to address this problem using switchable dampers which have a damping rate which can be varied to suit the current driving conditions.
Whilst these systems do address the problem, there is always a need for better control of such systems.
The present invention provides a vehicle suspension system for connecting at least one pair of wheels to opposite sides of a vehicle body, the system comprising a suspension associated with said at least one pair of wheels and arranged to allow articulation movement of said at least one pair of wheels relative to the body and to provide adjustable resistance to said articulation movement, sensors arranged to measure movement of the suspension, and a controller arranged to monitor said movement and to determine therefrom the level of said articulation movement and to reduce said resistance if said articulation movement reaches a predetermined level.
Preferably the adjustable resistance to articulation movement is an adjustable articulation stiffness. However, it could also be an adjustable damping rate provided by dampers which either damp all vertical movements of the individual wheels, or damp specifically articulation movements.
The measured articulation can be single axle articulation, that is the difference in ride height between the two front wheels, or the difference in ride height between the rear two wheels of a typical four-wheeled vehicle. Alternatively the measured articulation may be cross articulation, that is the difference between the articulation of the front wheels, and the articulation of the rear wheels.
Preferably the sensors are arranged to measure the ride height of each of said at least one pair of wheels and the controller is arranged to determine the level of articulation movement of said at least one pair of wheels from the measured ride heights.
Preferably the controller is arranged to determine a level of cross articulation movement between two pairs of the wheels, each pair being on opposite sides of the body, and to reduce said resistance if said cross articulation movement reaches a predetermined level.
The sensors may be arranged to measure the ride heights of each of both pairs of wheels, and the controller arranged to determine the level of cross articulation movement from the measured ride heights.
Preferably the controller is arranged to calculate a running measure of the level of articulation movement and to reduce said resistance if the running measure reaches a predetermined level.
Preferably the running measure is arranged to increase during periods when said level of articulation movement is high and to decrease during periods when said level of articulation movement is low.
Preferably the system further comprises a vehicle speed sensor arranged to measure a travelling speed of the vehicle, and the running measure includes a speed dependent offset arranged to cause it to reduce when the travelling speed of the vehicle is high.
Preferably the controller is arranged to increase the level of said resistance when the running measure falls below a predetermined level.
Preferably the controller is arranged to measure an instantaneous articulation displacement of the wheels, and running measure is a running average of the articulation displacement.
Preferably the controller includes a low pass filter and is arranged, when determining the level of said articulation movements, to filter out articulation movements of a frequency higher than a predetermined limit frequency.
Preferably the body has a natural frequency of vibration on the suspension and said limit frequency is of the order of said natural frequency of vibration, which is desirably of the order of 2 to 3 Hz.
Preferably the articulation sensors are arranged to measure the instantaneous articulation displacement of the wheels and to reduce said resistance only when said displacement is less than a predetermined limit.
Preferably the controller is arranged to detect when the vehicle is travelling on a side slope, and, in response to detection of a side slope, to increase said resistance.
The present invention further provides a vehicle suspension system for connecting at least one pair of wheels to opposite sides of a vehicle body, the system comprising a suspension associated with said at least one pair of wheels and arranged to allow articulation movement of said at least one pair of wheels relative to the body and to provide adjustable resistance to said articulation, a side slope detector arranged to detect when the vehicle is travelling on a side slope, and a controller operably connected to the suspension and the side slope detector and arranged to increase said resistance in response to detection of a side slope.
Where said resistance is adjustable between a high level and a low level, the controller is preferably arranged to detect when the vehicle is travelling on a side slope, and, if a side slope is detected when the resistance is at the low level, to adjust it to the high level.
Preferably the system further comprises a plurality of sensors arranged to send signals to the controller and the controller is arranged to use the signals to detect when the vehicle is travelling on a side slope.
The present invention further provides a vehicle suspension system for connecting at least one pair of wheels to opposite sides of a vehicle body, the system comprising a suspension associated with said at least one pair of wheels and arranged to allow articulation movement of said at least one pair of wheels relative to the body and to provide adjustable resistance to said articulation, a plurality of sensors, and a controller operably connected to the suspension and the sensors wherein the controller is arranged to receive signals from the sensors, to determine from said signals when the vehicle is travelling on a side slope, and to increase said resistance in response to detection of a side slopes.
Preferably said resistance is adjustable between a high level and a low level and the controller can be shut down and started up and is arranged: to measure an instantaneous articulation displacement of the wheels, on shut down to store the instantaneous articulation displacement of the wheels and the instantaneous level of said resistance, and on start up, if the instantaneous level of said resistance on shut down was the low level, to compare the instantaneous displacement with the stored displacement and, if they are substantially the same, to return the resistance to the low level.
The present invention further provides a vehicle suspension system for connecting at least one pair of wheels to opposite sides of a vehicle body, the system comprising a suspension associated with said at least one pair of wheels and arranged to allow articulation movement of said at least one pair of wheels relative to the body and to provide resistance to said articulation movement which resistance is adjustable between a high level and a low level, and a controller for adjusting said resistance wherein the controller can be shut down and started up and is arranged: to measure an instantaneous displacement of the wheels, on shut down to store the instantaneous displacement of the wheels and the instantaneous level of said resistance, and on start up, if the instantaneous level of said resistance on shut down was the low level, to compare the instantaneous displacement with the stored displacement and, if they are substantially the same, to return the resistance to the low level.
Preferably the controller is arranged, if said instantaneous displacement and said stored displacement are not substantially the same, to measure an instantaneous articulation displacement of the wheels and, if it is below a predetermined threshold to return the resistance to the low level.
Preferably the controller is arranged, if said instantaneous articulation is above said predetermined threshold, to delay returning of said resistance to said low level until the instantaneous articulation next falls to said predetermined threshold.
The suspension may include fluid filled suspension units associated with the wheels, with an adjustable fluid interconnection provided between the units, the controller being arranged to reduce said resistance by adjusting the interconnection. The fluid may be air or hydraulic fluid.
Alternatively the suspension may include a split anti-roll bar having two halves which can be de-coupled from each other to reduce said resistance.
The present invention further provides a vehicle suspension system for connecting a pair of wheels to opposite sides of a vehicle body, the system comprising a suspension associated with said wheels and arranged to allow articulation movement of wheels relative to the body and to provide adjustable resistance to said articulation movement, ride height sensors arranged to measure the ride height or each of the wheels, and a controller arranged to monitor the measured ride heights and to determine therefrom a level of said articulation movement and to reduce said resistance if said articulation movement reaches a predetermined level.
The present invention still further provides a vehicle suspension system for connecting two pairs of wheels to opposite sides of a vehicle body, the system comprising a suspension associated with said wheels and arranged to allow articulation movement of each of said pairs of wheels relative to the body and to provide adjustable resistance to said articulation movement, ride height sensors arranged to measure the ride height of each of the wheels, and a controller arranged to monitor the measured ride heights and to determine therefrom a level of cross articulation movement of the wheels, and to reduce said resistance if said level of cross articulation movement reaches a predetermined level.
Preferred embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings.